1. Field of the Invention
The present invention relates to a charged particle measuring device and a measuring method for measuring charged particles such as low-level alpha rays, and in particular to a charged particle measuring device and measuring method suitable for the quantitative analysis of charged particles such as low-level alpha rays in various materials.
2. Description of the Related Art
Conventional art will be described in particular for the measurement of alpha rays among various types of charged particles.
As conventional technology, there is a gas flow-proportional counter type low-level alpha ray measuring device mentioned in xe2x80x9ca super-low-level alpha ray measuring devicexe2x80x9d, Electronic Material, August 1988, p. 91. This apparatus is a gas flow-proportional counter with a detection area of 1000 cm2, and a detector where cathodes are arranged above and below a multiple wire type anodes disposed at the center. A test sample is directly put into the detector, and is placed closely to the lower side of a grid-like lower cathode. A counting gas is flown at a rate of about 200 ml per minute, the counting gas being a PR gas which is a mixed gas of argon and methane, and several thousands volts of DC voltage is applied to between the anodes and cathodes. When an alpha particle enters into the detector, the gas is ionized, and a short pulse current flows. Hence, the number of alpha particles is counted by converting this current into a voltage pulse and counting them.
In order to take countermeasures against problems such as a soft error phenomenon where stored charges in a semiconductor memory are reversed by alpha particles, the problem being caused by semiconductor memories becoming finer, it is important to perform a nuclide identification and low-level quantitative analysis of a disturbance alpha ray that a trace natural alpha emission element included in various material emits.
Although it can easily measure a sample with a large area, the above-described conventional gas flow-proportional counter type low-level alpha ray measuring device needs to apply several thousands volts of DC voltage to between the anodes and cathodes of the detector, and needs to perform measurement while flowing PR gas as the counting gas. Hence, the apparatus becomes large in size.
In addition, in the performance of alpha ray analysis, there are major defects that energy resolution is inferior, that discriminating measurement of an alpha ray nuclide is not possible, and that a background discrete value cannot be made small, and hence, lower-level alpha ray measurement cannot be performed.
A first object of the present invention is to provide a charged particle measuring device with high sensitivity that can efficiently measure charged particles such as a low-level alpha ray whose nuclide is identified, and a measuring method thereof.
A second object of the present invention is to provide a charged particle measuring device that can realize the measurement of charged particles such as a lower-level alpha ray, and a measuring method thereof.
A third object of the present invention is to provide a charged particle measuring device which can reduce the background discrete value, and a measuring method thereof.
A fourth object of the present invention is to provide a charged particle measuring device which is not a large-scale apparatus, but can realize the measurement of charged particles such as a lower-level alpha ray, and a measuring method thereof.
To achieve the above-described objects, a charged particle measuring device according to the present invention is characterized in comprising a measuring chamber having a sealing door which can be opened and closed, the measuring chamber comprising: a semiconductor detector; a radiation measuring circuit including a sample tray on which a measurement sample is placed so as to oppose to the semiconductor detector, a preamplifier, a linear amplifier, and a pulse height analyzer connected to the semiconductor detector; a charged particle emission amount arithmetic unit for performing the quantitative analysis of charged particles with an output signal from the radiation measuring circuit; a display unit for displaying the analysis result of the charged particle emission amount arithmetic unit; and including: an evacuation pipe line for discharging air to the measuring chamber; and a pure gas supply pipe line for performing the supply and replacement of a pure gas.
In addition, a charged particle measuring device according to the present invention is characterized in comprising a measuring chamber, the measuring chamber comprising: a semiconductor detector; a measurement sample placed so as to oppose to the semiconductor detector; a radiation measuring circuit which includes a shield shutter that is arranged between the semiconductor detector and the sample and shields charged particles entering from the sample at the time of background measurement, and is connected to the semiconductor detector to perform spectrum analysis; a charged particle emission amount measuring device which performs the quantitative analysis of charged particles with an output signal of the radiation measuring circuit; a display unit for displaying the analysis result of the charged particle emission amount measuring device, and including an evacuation apparatus and a gas replacement apparatus, which are connected through an exhaust pipe which communicates with the measuring chamber.
Furthermore, a charged particle measuring method according to the present invention is characterized in comprising the steps of: arranging a sample tray on which a test sample is placed so as to oppose to a semiconductor detector in a measuring chamber having a sealable door which can be opened and closed; performing cycle purge for a predetermined number of times with a pure gas by an evacuation apparatus and a gas replacement apparatus which are connected through an exhaust pipe which communicates with the inside of the measuring chamber, and thereafter measuring a charged particle emission amount by a radiation measuring circuit which includes a preamplifier, a linear amplifier, and a pulse height analyzer that are connected to the semiconductor detector, and a charged particle emission amount arithmetic unit for performing quantitative analysis of charged particle with an output signal from the radiation measuring circuit, and setting the charged particle emission amount as a background measurement; and calculating a charged particle emission amount value which is obtained by subtracting the background measurement from a measurement of the charged particle emission amount obtained by measuring a charged particle emission amount after placing the sample on the sample tray and performing cycle purge for a predetermined number of times with a pure gas.
Moreover, a charged particle measuring method according to the present invention is characterized in comprising the steps of: arranging a measurement sample so as to oppose to a semiconductor detector in a measuring chamber; shielding charged particles entering from the measurement sample by a shield shutter between the semiconductor detector and the sample; performing cycle purge for a predetermined number of times with a pure gas by an evacuation apparatus and a gas replacement apparatus which are connected through an exhaust pipe communicating with the inside of the measuring chamber, and thereafter measuring a charged particle emission amount by a radiation measuring circuit which is connected with the semiconductor detector and performs spectrum analysis, and a charged particle emission amount measuring device which performs the quantitative analysis of charged particles with an output signal of the radiation measuring circuit, and setting the charged particle emission amount as a background measurement; and calculating a charged particle emission amount value which is obtained by subtracting the background measurement from a measurement of the charged particle emission amount obtained by measuring a charged particle emission amount entering from the sample, by opening the shield shutter.